It is a 256KiB flash with 4 KiB erase sectors
and 64KiB overlay blocks.

This is the one available on Hardkernel's Odroid U3 shield.
Signed-off-by: NAlexis Ballier <aballier@gentoo.org>
[Brian: seems like this does NOT require the usual SST_WRITE hacks]
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>